The present invention relates to a radio unit casing for a portable radio unit with a single high-gain antenna unit for transmitting and receiving radio signals within a wide scan range in a satellite communication system.
The name portable radio unit includes all portable equipment intended for radio communication, like mobile phones, transceivers, pagers, telex, electronic notebooks and communicators. These equipments can be used in any type of radio communication system, such as cellular networks, satellite or small local networks.
One type of radio communication is cellular mobile communication where portable radio units communicate with each other or with fixed units through mobile basestations on the ground. Portable radio units, for example mobile phones, which typically transmit and receive signals at a frequency of approximately 900 Megahertz or 1800-1900 Megahertz (MHz), are well known.
Recently it has become important for another type of radio communication, i.e. satellite communication.
In the near future, we will foresee communications by satellites directly to portable radio units. The satellites can reach portable radio units in areas where cellular communication is unavailable due to the lack of necessary cellular towers, base stations or compatible standards. Such satellite communications could allocate to the 2 Gigaherz (GHz) band and the 20/30 GHz bands. Several systems with high data rates (64 kbps and 2 Mbps) are in the planning stage.
The satellites of the systems can be of different types such as GEO (Geostationary Earth Orbit), ICO (Intermediate Circular Orbit), LEO (Low Earth Orbits) or HEO (Highly Elliptical Orbit).
It is recognised that for cellular and satellite mode communication different types of antennas are necessary since cellular antennas usually are linearly polarised and satellite antennas usually are circularly polarised. A further difference is that the satellite communication mode involves a directional component, where link-margin is increased when the satellite antenna on the portable radio unit is pointed toward the satellite, and the cellular communication mode does not usually have such a directional component. Thus, the positioning of the satellite antenna in the portable radio unit is very important, as is the construction of the satellite antenna.
One example of a portable radio unit is a portable phone. Flip covers for portable phones have generally been used to protect the keypad or the display. In some applications, though, the flip cover has been utilised to house an antenna (e.g. U.S. Pat. Nos. 5,337,061, 5,542,106, 5,451,965).
The European patent application with publication number EP 752 735 describes an antenna system of several individual antennas attached to or integrated in a housing of a mobile telephone. The high frequency power emitted from each antenna is individually controllable. The antenna system measures the wave impedance for each antenna and steers the emitted power to those antennas which measures the impedance of free space propagation. The purpose of this antenna system is to avoid radiation on the head of the user. The antenna system also gives a receive diversity (not mentioned in the description or claimed).
The Japanese patent with publication number JP 56-168437 describes a portable radio device with two separate micro-strip antennas attached on a housing of the radio device. Both antennas are arranged on the same side of the radio device. One of these antennas can be used for both transmission and reception and the other antenna is only used for reception which entails reception diversity. The purpose of this patent is to eliminate the risk of breaking an antenna by attaching two microstrip antennas on the surface of the housing of the radio device.
The PCT patent application with publication number WO 95/04386 describes a composite antenna for hand held communications applications comprising at least two individual antennas. These antennas are spaced from each other at a specified distance.
As will be seen herein, each of the antennas disclosed in these patents is of a different construction than the radio unit casing with the satellite antenna of the present invention.
The present invention meets a number of problems related to antennas on portable radio units in satellite communication systems.
One problem is the integration of an antenna unit with transmit and receiving means in a casing where the area of the antenna unit has to be limited to the geometrical dimensions of the portable radio unit.
Another problem is to obtain a high antenna directivity in spite of the limited area available on a radio unit casing of a portable radio unit.
A further problem occurs when the portable radio unit is moved or turned in such a way that the angle between the beam direction pointing at the satellite and the aperture normal of the antenna unit becomes large. This requires that the antenna unit in the casing must be designed to have an antenna gain almost independent of the radio unit position.
Yet another problem occurs when the antenna in the portable radio unit has to scan a wide portion of the upper hemisphere to locate satellites. This requires that the scan volume for the transmit and receiving means has to be identical and that the scan range is wide.
A similar problem is that the antenna in the portable radio unit has to track the satellite with its transmit and receiving beams during movement of the satellite and/or the portable radio unit. This requires that the antenna in the portable radio unit must have the capability to both transmit and receive with beams pointing in substantially the same directions.
Another problem occurs when radio waves between the satellite and the portable radio unit are weak due to low output power from the satellite or the portable radio unit, or there is an attenuation in the radio wave propagation path between the satellites and the radio unit antenna. This requires higher radio unit antenna gain to achieve extra link margin.
Yet another problem is to avoid that the beam of the antenna unit is scattered by the user of the portable radio unit.
In light of the foregoing, a primary object of the present invention is to provide a radio unit casing with an integrated conformal antenna capable of operating in a satellite communication mode.
Another object of the present invention is to provide a radio unit casing with an integrated antenna that has a nearly constant gain in the whole scan range and the ability to search for and to track individual satellites.
Yet another object of the present invention is to provide a radio unit casing with an integrated antenna for a portable radio unit in which the transmitting and receiving means of the antenna unit shares the same aperture and scan volume.
Further objects of the present invention is to provide a radio unit casing for a portable radio unit with an integrated antenna unit, where said antenna unit has a scan range of at least half the upper hemisphere and a highly directional antenna radiating pattern with steerable transmit and receive beams.
Another object of the present invention is to obtain a widespread antenna aperture area which faces many directions in the radio unit casing to maintain a reasonable receive and transmit quality even at large scan angles.
Still another object of the present invention is to use the high gain and the beam control for satellite tracking in the radio unit to divert the beam from the antenna unit away from the user of the portable radio unit, to reduce powerless and avoid scattering.
A further object of the present invention is to obtain highest possible antenna gain within the constraints of the portable radio unit""s geometrical dimensions to increase the margin in the link budget.
Another object of the present invention is to enable the antenna unit to establish a beam sufficiently sharp to select one of several satellites which can be viewed from the site of the portable radio unit.
In accordance with the present invention, a radio unit casing is disclosed in which a conformal antenna array is arranged in the radio unit casing.
More specifically, the antenna array comprises a number of adjacent antenna array surfaces with transmission and reception means which are arranged in the radio unit casing in such a way that the antenna array surfaces face in a multitude of directions. More than one of these antenna array surfaces are co-operating simultaneously to create a beam for transmitting or receiving radio signals. The antenna unit is conformal to the portable radio unit, has no movable parts and comprises interleaved antenna radiating elements, e.g. patches or slots, in a multi-layer structure.
Advantages with the present invention are that the beams of the antenna array are highly directional, they have a high terminal antenna transmit and receive gain and identical scan volumes. This entails that the portable radio unit can track individual satellites and establish a communication link.
Another advantage is that the antenna array in the radio unit casing faces more than one direction which entails an almost radio unit positioning independent antenna gain. This also entails a wide scan range in which a beam from the antenna array can scan for satellites in the upper hemisphere.
Other advantages are that the beams of the antenna unit avoids to be scattered by the user and that the antenna unit in the radio casing has no movable or protruding parts.